This invention relates to a photo- or heat-curable resin composition suitable for insulating a printed wiring board and to a multilayer printed wiring board containing an insulating resin layer formed from said photo- or heat-curable resin composition.
In recent years, the on-going miniaturization of electronic instruments has led to the development of a multi-level system for printed wiring in order to attain a higher degree of integration of electronic devices and the so-called build-up process which is put into practice by forming an insulating layer and a conductive layer alternately and laminating them together has come into frequent use. And here, high reliability is demanded for the resin materials to be used for insulation. Moreover, it is often the case that a printed wiring board is covered with an insulating layer to protect the surface or the mounted chips.
In the use of insulating materials based on organic resins in multilayer printed wiring boards, however, the organic resins differ greatly in the thermal expansion coefficient from the active parts such as semiconductor devices and the passive parts such as capacitative elements and resistors and, still more, from substrates such as sintered alumina materials, epoxy resins on glass cloth formed by impregnating glass cloth woven from glass fibers with epoxy resins, and silicon wafers; in case a large thermal stress results from the difference in the thermal expansion coefficient between the organic resins and other components, the stress causes cracking and splitting apart of semiconductor devices, capacitative elements, and conductive wirings and the affected devices cease to function normally.
Now, a practice of incorporating fillers in resin insulating materials is known from old and the incorporation of fillers in the resin components constituting the resin insulating layers of multilayer wiring boards is also known. In JP 09-148748 (1997)A1, for example, a filler is used for roughening the surface of a resin insulator in order to improve the adhesion of resin insulator to wiring; however, the filler here is used not only for the object different from that of this invention but also at a high rate of incorporation on the order of 5-50% by weight and the practice as described here cannot manifest a sufficient effect in the thermal shock test which is a typical reliability test.
On the other hand, JP 10-242650 (1998)A1 has an object of reducing cracking in the thermal shock test and attempts to realize this by reducing the thermal expansion coefficient of an insulating material by adding a filler. In this case again, the content of the filler is high on the order of 10-95% by weight and fine patterns are difficult to obtain when the resin insulating layer is processed.
Wet plating and dry plating are known in the manufacture of multilayer printed wiring boards by a process such as the build-up process; the former requires the uneven condition in practice which makes its use difficult in a high frequency region and the latter is gaining favor.
Accordingly, an object of this invention is to provide a photo- or heat-curable resin composition which cures into a film of high reliability as tested by the thermal shock test which is a typical test for reliability of substrates as a resin composition for forming a resin insulating layer in a wiring board. Another object of this invention is to provide a resin composition which can be processed to yield fine patterns. A further object of this invention is to provide a cured resin which is heat- and solvent-resistant and suitable for use as an interlayer insulating layer in a multilayer printed wiring board.
The present inventors have conducted extensive studies to solve the aforementioned problems, found that incorporating in a resin a fine filler with its particle diameter controlled in the specified range contributes to produce an effect of preventing the formation of minute cracks when the resin is used as an insulating layer in a wiring board, and completed this invention.
This invention relates to a photo- or heat-curable resin composition which is intended for forming an insulating layer in a multilayer printed wiring board and comprises 0.1-5 parts by weight of an inorganic filler with its average particle diameter controlled in the range 5 nm-0.5 xcexcm per 100 parts by weight of the resin-forming component.
Moreover, this invention relates to the aforementioned photo- or heat-curable resin composition comprising (A) 100 parts by weight of a photopolymerizable unsaturated compound represented by the following general formula (1) 
wherein R is a hydrogen atom or a methyl group, A is a group represented by the formula (2) 
(wherein R1 and R2 are hydrogen , an alkyl group with 1-5 carbon atoms, or a halogen) and X is xe2x80x94COxe2x80x94, xe2x80x94SO2xe2x80x94,xe2x80x94C(CF3)2xe2x80x94,xe2x80x94Si(CH3)2xe2x80x94, xe2x80x94CH2xe2x80x94,xe2x80x94C(CH3)2xe2x80x94,xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, 
or a single bond, Y and Z are respectively the residue of a polycarboxylic acid or its acid anhydride, and m and n are the number of structural units at a molar ratio (m/n) 0/100-100/0,
(B) 0-50 parts by weight of a compound containing an epoxy group, and
(C) 0-10 parts by weight of a photopolymerization initiator or sensitizer.
Still more, this invention relates to the aforementioned photo- or heat-curable resin composition comprising silica sol as an inorganic filler. Furthermore, this invention relates to a multilayer printed wiring board comprising a cured product of the aforementioned photo- or heat-curable resin composition as an insulating layer.